Tiled drawable sometimes stretches

I have a ListView whose items have a tiled background. To accomplish this, I use the following drawable xml:

<bitmap
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/tile"
    android:tileMode="repeat" />

Usually, this works. Sometimes, however, the src drawable isn't tiled, but stretched to fill the entire list item. (I've got several different tiles like this, and I use them mixed in one ListView. If there is stretching instead of tiling, it's never been in all of them at once, for what that's worth.)

I also tried to add android:dither="true" to that xml, since I read somewhere that without it there might be bugs. That didn't change anything.

Has anyone had the same problem? How did you fix it?